Systems relating to geothermal energy and the operation of gas turbine engines

ABSTRACT

A geothermal heat exchange system for use in a gas turbine power plant that includes an inlet plenum that directs a flow of air to a compressor that compresses a flow of air that is then mixed with a fuel and combusted in a combustor such that the resulting flow of hot gas is directed through a turbine, the geothermal heat exchange system comprising means for exchanging heat between a ground and the flow of air moving through the inlet plenum.

BACKGROUND OF THE INVENTION

This present application relates generally to gas turbine engines andapparatus, systems and methods related thereto. More specifically, butnot by way of limitation, the present application relates to apparatus,systems and methods for enhancing gas turbine energy performance by useof, among other things, geothermal energy.

With rising energy cost and increasing demand, the objective ofimproving the efficiency of gas turbine engines and more effectivelyexploiting renewable energy sources, such as geothermal energy, is asignificant one. Toward this aim, as described below, cost-effectivesystems may be developed to use the relatively constant temperaturefound beneath the surface of the earth to improve gas turbine engineoperation, particularly as it relates to hot and cold day operation.

As one of ordinary skill in the art will appreciate, the performance ofgas turbine engines may be negatively affected when ambient temperaturesare either too hot or too cold. For example, when the inlet airtemperature is too hot, the gas turbine heat rate increases and outputpower deceases, which, of course, decreases the efficiency of theengine. On the other hand, when ambient temperatures fall below acertain level, icing may occur. This may occur at the inlet to thecompressor, for example, on the inlet to the filter house, or the inletguide vanes or other similarly situated components. The icing may damageequipment or cause it to operate ineffectively. For example, icing mayprevent the IGV from operating correctly, which may negatively impactthe efficiency of the turbine engine.

Convention systems have been proposed for resolving these issues. Forexample, for hot day operation, some conventional systems propose theuse of a mechanical chiller system to cool the air entering thecompressor. This option is undesirable because the energy required tooperate the chiller significantly impacts the overall efficiency of thegas turbine engine as well as the high equipment cost associated withthe chiller. Another conventional system is an inlet fogging system,which includes injecting water vapor into the air entering thecompressor. The evaporation of the injected vapor decreases thetemperature of the air flow. However, the proper function of this typeof system is still at least somewhat dependent on ambient conditions andrequires the installation of costly hardware and control systems.Further, the addition of water to the engine flow path in this mannermay cause more rapid degradation and erosion of parts within the flowpath and, as such, generally increases maintenance costs.

For cold day operation, conventional systems generally include drawingenergy from the engine exhaust to raise the temperature of the airentering the compressor. Again, though, such systems require aninstallation of costly hardware and control systems. Further, to theextent that the energy in the exhaust may be used for other purposes,such as, for example, as the heat source in the steam turbine of acombined cycle plant, the diverting of a portion of the exhaust energygenerally decreases the overall efficiency of the power plant.

As a result, there remains a need for improved apparatus, systems andmethods for cost-effectively alleviating performance issues in gasturbine engines that occur during hot and cold day operation.

BRIEF DESCRIPTION OF THE INVENTION

The present application thus describes a geothermal heat exchange systemfor use in a gas turbine power plant that includes an inlet plenum thatdirects a flow of air to a compressor that compresses a flow of air thatis then mixed with a fuel and combusted in a combustor such that theresulting flow of hot gas is directed through a turbine, the geothermalheat exchange system comprising means for exchanging heat between aground and the flow of air moving through the inlet plenum.

The present application further describes a geothermal heat exchangesystem for use in a gas turbine power plant that includes an inletplenum that directs a flow of air to a compressor that compresses a flowof air that is then mixed with a fuel and combusted in a combustor suchthat the resulting flow of hot gas is directed through a turbine, thegeothermal heat exchange system comprising a plurality of heat pipesthat are configured to exchange heat between a location within a groundat a predetermined depth and the flow of air moving through the inletplenum; wherein the heat pipe comprises a two-phase heat transfer devicethat includes a sealed tube made of a material with high thermalconductivity both a hot end and a cold end; and the sealed tube isevacuated and backfilled with a small quantity of a working fluid.

These and other features of the present application will become apparentupon review of the following detailed, description of the preferredembodiments when taken in conjunction with the drawings and the appendedclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a section view of a gas turbine engine typical of the types ofturbine engines that may be used in power plants in which embodiments ofthe present invention may be used;

FIG. 2 illustrates a schematic plan of a gas turbine engine, therepresentation of which will be used to illustrate power plantsaccording to embodiments of the present invention;

FIG. 3 is a schematic plan illustrating the configuration of a gasturbine power plant according to an exemplary embodiment of the presentapplication;

FIG. 4 is a schematic plan illustrating a front view (i.e., into themouth of the inlet plenum) of the configuration of heat pipes in theinlet plenum according to an exemplary embodiment of the presentapplication; and

FIG. 5 is a schematic plan illustrating the configuration of a gasturbine power plant according to an alternative embodiment of thepresent application.

DETAILED DESCRIPTION OF THE INVENTION

Illustrative embodiments of the invention now will be described morefully hereinafter with reference to the accompanying drawings, in whichsome, but not all embodiments of the invention are shown. Indeed, theinvention may be embodied in many different forms and should not beconstrued as limited to the embodiments set forth herein; rather, theseembodiments are provided so that this disclosure will satisfy applicablelegal requirements. Like numbers refer to like elements throughout.

To describe clearly the invention of the current application, it may benecessary to select terminology that refers to and describes certainmachine components or parts of a turbine engine. Whenever possible,common industry terminology will be used and employed in a mannerconsistent with its accepted meaning. However, it is meant that any suchterminology be given a broad meaning and not narrowly construed suchthat the meaning intended herein and the scope of the appended claims isunreasonably restricted. Those of ordinary skill in the art willappreciate that often certain components may be referred to with severaldifferent names. In addition, what may be described herein as a singlepart may include and be referenced in another context as consisting ofseveral component parts, or, what may be described herein as includingmultiple component parts may be fashioned into and, in some cases,referred to as a single part. As such, in understanding the scope of theinvention described herein, attention should not only be paid to theterminology and description provided, but also to the structure,configuration, function, and/or usage of the component as providedherein.

In addition, several descriptive terms may be used herein. The meaningfor these terms shall include the following definitions. As used herein,“downstream” and “upstream” are terms that indicate a direction relativeto a flow of working fluid through the turbine. As such, the term“downstream” means the direction of the flow, and the term “upstream”means in the opposite direction of the flow through the turbine engine.Related to these terms, the terms “aft” and/or “trailing edge” refer tothe downstream direction, the downstream end and/or in the direction ofthe downstream end of the component being described. And, the terms“forward” or “leading edge” refer to the upstream direction, theupstream end and/or in the direction of the upstream end of thecomponent being described. The term “radial” refers to movement orposition perpendicular to an axis. It is often required to describeparts that are at differing radial positions with regard to an axis. Inthis case, if a first component resides closer to the axis than a secondcomponent, it may be stated herein that the first component is “inboard”or “radially inward” of the second component. If, on the other hand, thefirst component resides further from the axis than the second component,it may be stated herein that the first component is “outboard” or“radially outward” of the second component. The term “axial” refers tomovement or position parallel to an axis. And, the term“circumferential” refers to movement or position around an axis.

Referring now to the figures, FIG. 1 is an illustration of a conventiongas turbine engine 50. In general, gas turbine engines operate byextracting energy from a pressurized flow of hot gas that is produced bythe combustion of a fuel in a stream of compressed air. As illustratedin FIG. 1, gas turbine engine 50 may be configured with an axialcompressor 52 that is generally mechanically coupled by a common shaftor rotor to a downstream turbine section or turbine 54, and a combustor56 positioned between the compressor 52 and the turbine 54.

The compressor 52 may include a plurality of stages, with each stagehaving a row of compressor rotor blades followed by a row of compressorstator blades. Particularly, a stage generally includes a row ofcompressor rotor blades, which rotate about a central shaft, followed bya row of compressor stator blades, which remain stationary duringoperation. The compressor stator blades generally are circumferentiallyspaced one from the other and fixed about the axis of rotation. Thecompressor rotor blades are attached to the shaft such that, when theshaft rotates during operation, the compressor rotor blades rotate aboutit. As one of ordinary skill in the art will appreciate, the compressorrotor blades are configured such that, when spun about the shaft, theyimpart kinetic energy to the air or fluid flowing through the compressor52. The turbine 54 also may include a plurality of stages. A turbinestage may include a plurality of turbine buckets or turbine rotorblades, which rotate about the shaft during operation, and a pluralityof nozzles or turbine stator blades, which remain stationary duringoperation. The turbine stator blades generally are circumferentiallyspaced one from the other and fixed about the axis of rotation. Whereas,the turbine rotor blades may be mounted on a turbine wheel for rotationabout the shaft.

In use, the rotation of compressor rotor blades 60 within the axialcompressor 52 compresses a flow of air. In the combustor 56, energy isreleased when the compressed air is mixed with a fuel and ignited. Theresulting flow of pressurized hot gases from the combustor 56, whichgenerally is referred to as the working fluid of the engine, is thenexpanded through the turbine rotor blades. The flow of working fluidinduces the rotation of the turbine rotor blades about the shaft.Thereby, the energy of the fuel is transformed into the kinetic energyof the flow of working fluid, which is then transformed into themechanical energy of the rotating blades and, via the connection betweenthe rotor blades and the shaft, the rotating shaft. The mechanicalenergy of the shaft may then be used to drive the rotation of thecompressor rotor blades, such that the necessary supply of compressedair is produced, and also, for example, to drive a generator (not shown)to produce electricity.

FIG. 2 illustrates a schematic plan of a gas turbine engine 100, therepresentation of which will be used to illustrate power plantsaccording to embodiments of the present invention. As shown, the gasturbine engine 100 may include a compressor 52, a combustor 56, and aturbine 54. At the upstream end of the compressor 52, an inlet plenum112 may be located. The inlet plenum 112 essentially provides a channelthrough which a supply of air is directed into the compressor 52. Itwill be appreciated that the configuration of the inlet plenum 112 maycomprise many different configurations. As illustrated, the inlet plenummay be configured to have a relatively wide mouth that decreases incross-sectional area into a channel that directs a supply of air to theinlet of the compressor 52. Of course, in some gas turbine engineapplications, a significantly smaller structure may be used to providean inlet for the air entering the compressor 52. As such, as usedherein, inlet plenum 112 is meant to describe any structure, large orsmall, that is positioned upstream of one of the stages of thecompressor 52 through which at least a portion of the air entering thecompressor 52 passes. As one of ordinary skill in the art willappreciate, the inlet plenum 112 may include certain components, such asfilters, silencers, etc., that improve the function of it. However,because these components are not essential or preclusive to the functionof a power plant according to the present invention, they have beenomitted from the figures. As will be seen, the flexibility ofembodiments of the present invention allows that it may be incorporatedin a variety of ways into substantially any type of inlet plenum 112structure or directly into the compressor 52 itself.

FIG. 3 is a schematic plan illustrating the configuration of a gasturbine power plant 130 according to an embodiment of the presentapplication. Similar to the system shown in FIG. 2, the gas turbinepower plant 130 may include a compressor 52, a combustor 56, a turbine54, and an inlet plenum 112. According to the present invention, the gasturbine power plant 130 also may include a heat exchange device thatprovides for the exchange of energy between the flow of air in the inletplenum 112 or through the compressor 52 and the earth or ground 134. Asused herein, “ground” is meant to include any type of geothermal medium.In some embodiments, ground refers to the earth at a predetermined levelunderground, as shown in FIG. 3. As will be appreciated, the temperatureof the ground beneath the surface of the earth remains fairly constantregardless of the season. This is particularly true at depths betweenapproximately 25 and 500 feet beneath the surface of the ground. In someembodiments, shallower depths also may be used; for example, depthsbetween approximately 10 and 50 feet beneath the surface of the groundmay be appropriate for certain applications.

These relatively constant subsurface temperatures mean that the groundtemperature within these given depth ranges remains relatively cool yearround even in warm climate locations. For example, the groundtemperature of Atlanta, Ga. remains a fairly constant 62° F. throughoutthe year. At the other end of the spectrum, in relatively cold climatelocations, the ground temperature remains relatively warm even in thecoldest months of the year. For example, the ground temperature of NewYork, N.Y. remains a fairly constant 52° F. throughout the year. Asstated, “ground” also may refer to other types of geothermal mediums,such as a subsurface location in a body of water, such as a lake or ariver or the ocean.

As shown in FIG. 3, in one preferred embodiment, the heat exchangedevice may be one or more elongated heat transfer structures 136, suchas one or more pipes, that extend from a position within the ground(which, for example, may be a position in the ground below the earth'ssurface, a subsurface location in a lake, or other such position) to aposition within the inlet plenum 112. The heat transfer structures 136may be configured to efficiently transfer heat from a hot side (which,depending on the application as well as current ambient and groundtemperature conditions, may be either the ground or the inlet plenum) toa cold side (which, depending on the application as well as currentambient and ground temperature conditions, may be either the ground orthe inlet plenum). At the hot side and the cold side, the structure 136generally will include an outer surface that conducts heat well, such asa metallic surface. In addition, one end of the structure 136, which, asshown may be a pipe, may be placed within the ground at a desired depthsuch that it contacts the surrounding earthen material or water and heattransfer between the surrounding material and the structure 136 is asdesired. The other end of the structure or pipe 136 may be placed in theinlet plenum 112 such that the air flowing through the inlet plenum 112flows over and around it so heat transfer occurring between thestructure 136 and the air flow occurs at a desired rate.

In some embodiments, the elongated structure 136 of FIG. 3 may comprisea conventional heat pipe. A heat pipe is a two-phase heat transferdevice with a high effective thermal conductivity. A heat pipe generallyconsists of a sealed pipe or tube made of a material with high thermalconductivity such as steel, copper or aluminum at both hot and coldends. It can be cylindrical or planar, and, as discussed below, theinner surface may be lined with a capillary wicking material. Inconstruction, the heat pipe is evacuated and backfilled with a smallquantity of a working fluid such as water, acetone, nitrogen, methanol,ammonia, or sodium. Other types of inorganic materials also may be used.Heat is absorbed in the evaporator region by vaporizing the workingfluid. The vapor transports heat to the condenser region where the vaporcondenses, releasing heat to a cooling medium.

In some embodiments, the heat pipe of the current invention may be alooped heat pipe, i.e., a heat pipe with a wick structure that exertscapillary pressure on the liquid phase of the working fluid. The wickstructure may include any material capable of exerting sufficientcapillary pressure on the condensed liquid to wick it back to the heatedend. In some embodiments, the wick structure may be one of the commonwick structures used in conventional heat pipe applications, whichinclude a groove wick structure (i.e., a series of grooves the runlengthwise along the inner surface of the heat pipe), a wire mesh wickstructure, a powder metal wick structure, and a fiber/spring wickstructure. The heat pipe may not need a wick structure if gravity orsome other source of acceleration is sufficient to overcome surfacetension and cause the condensed liquid to flow back to the heated end.

As shown in FIG. 3, in some embodiments, the heat pipes 136 of thepresent invention may be aligned vertically. In this arrangement and inthe absence of a wicking structure, geothermal energy from the ground134 may be used to heat the flow of air into the compressor 52 (i.e.,the warmer ground end of the heat pipe 136 evaporates a working fluidthat condenses at the cold end of the heat pipe in the inlet plenum 132thereby heating the air flowing around it). This arrangement may be usedwhen the ground temperature exceeds the air temperature, which may beeffective during cold day operation in preventing ice formation onengine components.

According to an alternative embodiment of the present application, awick structure, as described above, may be employed so that thevertically aligned heat pipes of FIG. 3 still may be used when theground temperature is less than ambient air temperature. In this case,engine operators may desire to cool the ambient air being supplied tothe compressor. Instead of gravity returning the condensed fluid to thecold side of the heat pipe, the capillary pressure provided by the wickstructure overcomes gravity, wicking the condensed fluid upward from thecolder ground side to the warmer side inside the plenum. Once inside theplenum, the heat pipe absorbs heat from the passing air flow via theevaporation of the wicked fluid. Cooling the air in this manner, asdiscussed, generally increases the efficiency of the gas turbine powerplant and may be used when the ambient temperature is high to improveengine performance.

The advantages of using heat pipes for any necessary cooling or heatingseveral. First, heat pipes are completely passive heat transfer systems,having no moving parts to wear out. Second, heat pipes require no energyto operate. Third, heat pipes are relatively inexpensive. Fourth, heatpipes are flexible in size, shape and effective operating temperatureranges.

In operation, when ambient temperatures go below a desirable level, heatpipes having the configuration shown in FIG. 3 may be activated to pumpheat from underground to heat the air passing through the inlet plenum112. This, for example, may be used to prevent unwanted ice from formingon the inlet filter house or inlet guide vanes. On the other hand, whenambient temperatures go above a desirable level, heat pipes having theconfiguration shown in FIG. 3 may be activated to pump heat from the airpassing through the inlet plenum 112 into the ground. This, for example,may be used on hot days to increase the efficiency of the engine.

As shown in FIGS. 3 and 4, in some embodiments, the heat pipes may havea plurality of branches. The branches 138 generally increase the surfacearea for heat exchange with the earth.

FIG. 4 illustrates a front view of the inlet plenum 112 (i.e., into themouth of the inlet plenum 112) and demonstrates an exemplaryconfiguration of heat transfer structure 136 (in this case, heat pipes)within the inlet plenum according to an embodiment of the presentapplication. As shown, the heat pipes may be arranged vertically andextend from the interior of the inlet plenum 112 to a desired depthwithin the ground 134. A plurality of heat pipes may be evenlydistributed across the inlet plenum 112. In certain applications, moreor less heat pipes may be used.

Referring now to FIG. 5, an alternative embodiment of a gas turbinepower plant according to the present application is shown, a gas turbinepower plant 150. In this case, a secondary heat transfer structure 152is configured to exchange heat between the inlet plenum 112 and theexhaust of the turbine 54. A heat recovery steam generator 154 may bepresent in this type of power plant, as shown. A portion of the turbineexhaust may be diverted from the main flow via an exhaust by pass 155and directed through a heat transfer unit 156. Within the heat transferunit 156, the exhaust may heat the secondary heat transfer structure152. The secondary heat transfer structure 152, as shown, may connect tothe heat transfer structure 136, where the heat from the exhaust may bepumped into the inlet plenum 112. This configuration provides anadditional heating element to the power plant, which, as one of ordinaryskill in the art will appreciate, may be necessary for certainapplications. The secondary heat transfer structure 152 may compriseheat pipes consistent with the description above.

As stated, in preferred embodiments, the heat transfer structure 136 andthe secondary heat transfer structure 152 comprise heat pipes. In otherembodiments according to the present invention, the heat transferstructure 136 and the secondary heat transfer structure 152 may compriseother conventional heat transfer structures or systems. For example, aheat sink made from solid pipes of conductive metals may be used inplace of the heat pipes. While the two-phase heat transfer associatedwith heat pipes may be more efficient mode of heat transfer, the singlephase conductive heat transfer associated with certain solid materialsmay be sufficient for some applications. In other embodiments, a heattransfer fluid may be circulated via a pump through a circuit so thatthe fluid exchange heat between the ground 134 and the inlet plenum 112.In still other embodiments, a thermosiphon may be used. As one ofordinary skill in the art will appreciate, a thermosiphon is a mechanismsimilar to a heat pipe in which thermal energy is transferred by fluidbuoyancy rather than evaporation and condensation.

As one of ordinary skill in the art will appreciate, the many varyingfeatures and configurations described above in relation to the severalexemplary embodiments may be further selectively applied to form theother possible embodiments of the present application. For the sake ofbrevity and taking into account the abilities of one of ordinary skillin the art, all of the possible iterations is not provided or discussedin detail, though all combinations and possible embodiments embraced bythe several claims below or otherwise are intended to be part of theinstant application. In addition, from the above description of severalexemplary embodiments of the invention, those skilled in the art willperceive improvements, changes and modifications. Such improvements,changes and modifications within the skill of the art are also intendedto be covered by the appended claims. Further, it should be apparentthat the foregoing relates only to the described embodiments of thepresent application and that numerous changes and modifications may bemade herein without departing from the spirit and scope of theapplication as defined by the following claims and the equivalentsthereof.

1. A geothermal heat exchange system for use in a gas turbine power plant that includes an inlet plenum that directs a flow of air to a compressor that compresses a flow of air that is then mixed with a fuel and combusted in a combustor such that the resulting flow of hot gas is directed through a turbine, the geothermal heat exchange system comprising means for exchanging heat between a ground and the flow of air moving through the inlet plenum.
 2. The geothermal heat exchange system according to claim 1, wherein the means for exchanging heat between the ground and the flow of air moving through the inlet plenum comprises a heat pipe.
 3. The geothermal heat exchange system according to claim 1, wherein the means for exchanging heat between the ground and the flow of air moving through the inlet plenum comprises a heat sink.
 4. The geothermal heat exchange system according to claim 1, wherein the means for exchanging heat between the ground and the flow of air moving through the inlet plenum comprises a heat transfer fluid circulated via a pump through a circuit that passes through the ground and the inlet plenum.
 5. The geothermal heat exchange system according to claim 1, wherein the means for exchanging heat between the ground and the flow of air moving through the inlet plenum comprises a thermosiphon.
 6. The geothermal heat exchange system according to claim 1, wherein the ground comprises one of a position in the ground below the surface of the earth and a position beneath the surface of a body of water.
 7. The geothermal heat exchange system according to claim 1, wherein the ground comprises a position in the ground at a predetermine depth below the surface of the earth.
 8. The geothermal heat exchange system according to claim 1, wherein the predetermined depth comprises a depth of greater than 25 feet.
 9. The geothermal heat exchange system according to claim 1, wherein the predetermined depth comprises a depth between 10 and 50 feet.
 10. The geothermal heat exchange system according to claim 2, wherein the heat pipe comprises a two-phase heat transfer device that includes a sealed tube made of a material with high thermal conductivity both a hot end and a cold end; and wherein the sealed tube is evacuated and backfilled with a small quantity of a working fluid.
 11. The geothermal heat exchange system according to claim 10, wherein working fluid comprises one of water, acetone, nitrogen, methanol, ammonia, and sodium.
 12. The geothermal heat exchange system according to claim 10, wherein the heat pipe is substantially vertically aligned and comprises a wick structure, the wick structure comprising a material that is configured to provide a desired capillary pressure on the condensed working fluid.
 13. The geothermal heat exchange system according to claim 10, wherein the wick structure comprises one of a groove wick structure, a wire mesh wick structure, a powder metal wick structure, and a fiber/spring wick structure.
 14. The geothermal heat exchange system according to claim 10, wherein the heat pipe is configured to transfer heat from the ground to the flow of air through the inlet plenum on cold days so that undesired ice formation is avoided.
 15. The geothermal heat exchange system according to claim 10, wherein the heat pipe is configured to transfer heat from the flow of air through the inlet plenum to the ground on hot days so that the efficiency of the gas turbine power plant is increased.
 16. The geothermal heat exchange system according to claim 10, wherein the heat pipes comprise a plurality of branches in the ground.
 17. The geothermal heat exchange system according to claim 10, wherein a plurality of heat pipes are vertically aligned and substantially evenly distributed across the inlet plenum.
 18. The geothermal heat exchange system according to claim 10, further comprising means for transferring'heat between a flow of exhaust from the turbine to the inlet plenum; wherein the means for transferring heat between the flow of exhaust from the turbine to the inlet plenum comprises a heat pipe.
 19. A geothermal heat exchange system for use in a gas turbine power plant that includes an inlet plenum that directs a flow of air to a compressor that compresses a flow of air that is then mixed with a fuel and combusted in a combustor such that the resulting flow of hot gas is directed through a turbine, the geothermal heat exchange system comprising a plurality of heat pipes that are configured to exchange heat between a location within a ground at a predetermined depth and the flow of air moving through the inlet plenum; wherein the heat pipe comprises a two-phase heat transfer device that includes a sealed tube made of a material with high thermal conductivity both a hot end and a cold end; and wherein the sealed tube is evacuated and backfilled with a small quantity of a working fluid.
 20. The geothermal heat exchange system according to claim 10, wherein the heat pipe is substantially vertically aligned, extended from the location within the ground to a position within the inlet plenum; and wherein the heat pipe includes a wick structure, the wick structure comprising a material that is configured to provide a desired capillary pressure on the condensed working fluid such that, in use, the heat pipe transfers heat from the flow of air through the inlet plenum to the ground on hot days so that the efficiency of the gas turbine power plant is increased. 